Loud speaker



C. MIDHAT LOUD SPEAKER Aug. 22, 1933..

Filed June 13. 1931 2 Sheets-Sheet fl C. MIDHAT LOUD SPEAKER Aug. 22,1933.

2 Sheets-Sheet 2 Filed June 13. 1951 ffy, f

Patente-d Augzz, 1933s Y L. l n `1,924,063, 1

i UNITED STATES PATENT, Nerica e o I 'e l 1,924,063',"

. v@norm SPEAKER y Chakir IVIidhat, Berlin-Eichkamp,,(emil'af` f.Application .time 1 3, 19,31, serial No. 544,057,'anaf 'I f in GermanyJune 24, 1930V l i j Y10 cilaiiilslicl.1814-31.)J Y Thisinventionrelates 'to further improvement designed this,` Way can beemployedalsofffoi'" of Aloudspeakers `of lthe type 'described in my thehousngcf the receiving .o ramplifying ap- United Statespatelntapplications `Serial Numparaitus,` which is impossible withfresonancenber 321,256, .filed blow/embr-:r4 22, 1928, issued as Abodies madeaccording to myapplication Seriall i 5 Patent #1,829,909, dated November3, l931,.and `Number 442,430 as inthislatter case ;the parts 6 SerialNumber 442,430,led April 7,1930, issued constituting` the borg' are l sounited with one as' Patent #1,829,930, dated November' 3, 1931,4 anotherby glueing that'theiinterior thereof 'is' in which,besidesalarger-surface diaphragm, also not accessible. .Y Y 1 aplurality of strings extending under tension'over In the' constructionalforms of the'loudspeaker v a resonance body, is caused to oscillate.`The as shown A.and described'insaid two former ap` 6 ,5 V

hereinafter. irstly, 'stretchingthe stringsandjtuningfthem 7o BOexpensive resonance Wood is used. This draw- 'tal dead Weight-,

present improvementsrelate to theconstruction plications all strings areconnected with one of the resonance body, the form 'of tensioning ofandthe? at 011e' .end b y amember specially pro-V thestrings, andalsothe coupling of the strings vided forthis purpose, vThis arrangementsuf-v with the driving unit, as' is all `fully described fers", however,from trieI following drawbacks:

. 'In' my` above-mentioned application VSerial to 'thede'sred pitch'lisvcircumstantial andre:

Number 442,430 l haveshown a constructional mires much` time, begausethestretching or form of the loudspeaker in which the resonance 'tighteningon" any one'of the `strings exerts a boxsurrounds the rim ofthediaphragm like 3f certain" effect' also uponvthe vother strings,'thatlfis Y baffle boad both faoee ofi the diaphragm Te', to say,affects the tuning thereoff'Secondly, the 7 5 o foaming free, All parteof the Tl"eso-ence body comparatively'. great Vweight of lthememberconwhich are made of Wood particularly'suted for,` Begging theStrips' with. one notherjs gtateu resonance purposes, are, in thatconstructional 'is ofA unfav'orame neue-fige; As, this member," fermunited with one another by gluemg inthe' is` subjected @tothetensilefstress Vof all' strings,4V

manner "knownv with ordinary stringed instruf it mugt GnSSt-yof a "Veryfsoldand ther 0 mentes@ as to constitute a unitl Y fore, heavy metal,such-as iron, brass or therme, o This menne? of composing the resonancebodyi v Besides, .the 4weight oflsaid' cennectin'g. member althoughpractically valuable, suffers nevertheand theWeighUjO-f thjfasteningknots .of theY less from 4the drawback that tool much of the(StrngS'jonjDnanthr toonsttute dammenback is detrimental for the reasonthat as,`in With my present' mproed'loudspeakth ome? to etten'thedesired-effect VZf an increase ldrawbacks mentioned, in the precedinglines are @strengthening of the resonance in the deeper ,obviated by'anothern manner ofestretching and 'tone ranges' 'this effect Will be thebetter at'v fastening the strings'in ,that,`whic]r1`is,thelchiejLtained, the larger the resonance body is. y featu O f thm mpOVementbothends Ofeah AV40A by lconnecting this front wall with the other part Thispermits Y Stretching each string independ f manner presents twoA moreimportant advan-V Wth present improved construction o f the stringereaixed to the resonance body,- `'whereas loudspeaker m qustlon the mstmentloped a suitable portioneoff their middle partsis cou-j drawback hasbeen doneA away .with vby making pled with the living unit by means of aclamp; only the front wall of good resonance Wood, and 'mgdevicespecially designed for :f5-nis purposeof the. lresona'tlxpox; that'is .made of I a' 'cheap ently of vall other strings so thatalsothetuning material and 1s rlgid 1n itself in such ,a manner of myone of the Strings does not affect the- ?hat its capabttylto oscme is,not-in the least pitch of the othery stringsl and furthermoretheIimpaired. Designing theresonance box` 1n this Clamping memhr ,o-,deviscompie-tek, reg 100, tages, in that, inthe rst place, the manufactureheVed fglfthfe nelthf Slllevgmf ojf the. loudspeaker Yis renderedcheaper owing.v .Caff C2 Y O hard mbbefofthe like, l Y not only to thecheaper material used for a large msArs-v 1re. dy men, (inscribed mlm;-applca fo pm thereof but also through economy m Work non sriallnumbr442 43o it" is 'with iouaspeaisv` l105 I 0 v as onlythe front wallwhichV isthe resonance` STS, hgvng Strings aiuta tothe ,pumoq ,to

A ll ned be anuf tured iter the` Y gproepllrinciles"follnlwed theAblilding of eouperonly'the daphagm rigidly With the erw* stringedinstruments, whereas theV entire other ing unit, Wllea the GS ClllatlOlSare tansfltfeod partof theboX can bemanufacturedin joinery '00 theStI1hg,S,` }1 1`? weakened Sbte- ,T h 1S 1S, manner; in thesecond'place, a'resonance body accordingto the above ref erred to-application 11,O

Y usual'design is employed.

vmany harmonics.'` I employ, when using a driving device withlargeeffected in this wayA that the memberv connecting the strings with oneanother leans against the moving part of the `driving unit with a slightelastic pressure. A presupposition for this man- Vner oftransmitting'the oscillations is this that the inovingpartV of thedrivingunit is elastically suspended, as is the case withjelectromagnetic driving units,v and that being so, said'manner oftransmitting the oscillations is not applicable where an electrodynamicdriving unit of the On the-other hand,

the rigid coupling of the strings with the electro`` dynamic drivingVunit is not suited because,

owing to theplarge amplitudesoi the oscillatory coil of the drivingunit, the loscillations of the strings become too strong whereby theimpres sion is caused Ythat,` the reproduction contains toov In` view ofthat drawback;

oscillatory amplitude, anotherform of :the transn mission of theVoscillations, .the arrangement and combination being such that, althoughlthere is afcoupling `between the "driving devicev and the strings,rstill, this isY not, as hitherto, a rigid coupling, but ismcre orlesselasti'cally yieldableY so that .the Y oscillations -are transrriittedlto strings only in'an eneebled state.

The. invention A.is illustrated ldiagramatically the and by. way "ofexamples on the' accompanyingr` drawings, on Which'ligure lis a front--viewv of a loudspeaker vdesigned according, to this` invention, aportion on the left hand side Vof lthe figure being fremoved for want oispace, thatV portion' -being just such a one as the correspondingportion voriY the` righthand side kof (the samev figure. FigureZ ischiefly a `verticalsection in the plane II--YIIv of Fig.V 1or1l'y theuppermostpart ofthe f figure being shown in side-view. Figure .3 lis aperspective View" ofthefmiddle portions of 'two sets of stringswhich'cross'one another, together-.

With the -Yconnectingmernbers for said strings,

or sets kof strings,` this, i'gure being drawn to ian enlarged scalerelatively to Figs. land 2.

1 ure 4 is an enlarged view'of the partsfvisible in vandinay rbemade ofany ordinary wood or or" good resonance.

ing lis illustrated in ,Fig. 2.

VVthefiniddle portion of Fig. 2, theigure showing the coupling ofthestrings withthejmoving member ofthe drivingdevice. And Figures 5 and 6show ,a simpliiied constructional formcf the loud? ,Y speakerinfront-view and in section;I all 'asli'ully v described hereinafter.

' In` Figsyl and Y2,7i2 denotes lthe frontk wall which is designed as aresonance board and consists ofra kind offwood having anv appropriatelyThe transverse ledges 6 `gluedy j to Asaid front wall 2k serve in'lnownmanner as reinforcement of the.same. 3 denotes thereark wallvwhich isdesigned `as a-rigid .barile` board anymther cheap'material suited for'the purpose and as also otherwise used for making ordinary baieboardaf tY. y The'resonan'ce board 2 isafrlxed to the'rigid part ofthe boxpreferably in such amanner that it can oscillate freely and Withoutanyimpedi-Y. ment, without transmitting a partworth inentioning of itsoscillatory energy mechanically to the rigid part. vAn example for suchay fasten- To the vtapering rims of the rescnanceboard are `glued ledges7 which consist of resonance .wood and'A by means of which theresonance,boardissecured vto said rigid part at a few points bymeansvofscrews 'j or the-like. The ledges 7 form at the same time a part of theside walls of the box. Whereas surrounds thev diaphragm 1 must belappropri- Vthus formed frame which lies next to the electropart,unimpededly lin the oscillations, its aperp Y f the other part 5 isrigid and is iirmly connected with ythe rear wall of the box. Y Y' Thatpart of the Yrigid rear, wall which carries' the driving device isinsertedas a separate part; and extends forwardly so much that its forcemostportion is located practically in the immediate neighbourhood of theresonance wall at theV .front of the box. ThisQseparate part 3EL is.shaped like a truncated pyramid or cone and it need-f notindispensablybemade lof Wood, but maybe made Valso ofa suitable metal,as is indicated in Fig'. 2,` butlthe`sheet-metal must 'A i v besufficiently thick and rigid.

Asappears from my application Serial Number'lZAS--loudspeakers havealready been pro-A vided lwith a resonance body arranged similartoabal'e board and servingalso for theampliiication ofthe airoscillations, chieiiy those of the lower".y frequencies, which is duetothe unequal propagation cir the airV oscillations' of .k differentfrequencies. In this` way the resonance .body

Ais*not*affected* bytheL oscillations that spread* straightway inthedirection "of the' diaphragm axis, Whereas the more or' lessdeflectedair oscillations Aof, the lower frequenciespush upon theresonance body and causeit to take part inthe oscillations.-

In order to lprovidetliat said presupposition-l" 'k viathe resonancebody taking part inthe oscillationsfonly at Vthe lower frequencies-be`wel1 fulfilled; caremust be takenthat also the air contained'in thenteriorof the box is'not clifrectlyfiniiuenced'or affected bythe4diaphragm oscillations. For this reason the Walle which ately thick sothat the interiorofY Athe box is separated from the diaphragm in asoundpro'of manner. This wall .which surrounds the dia-v phragm may be,what is suited to the purpose in` View, so ldesigned that it can serveat'the same time as a frame which connectsthe diaphragm with theelectromagnet' 9, vas isV the.

case in the example'shown. That part of the inagnetis provided withapertures 10 in known manner.r 'Y K .n ,i v.

. .In order to enable the resonance body to take v ture is made a littlepasses through it. .A v

In Fig. 2 there are indicated by arrows also suchair'oscillations thatarise during the re-V production of a lov/crotone yand during vthe' forlarger than vthe'wall 4 that ward movement of thediaphragm. kItis easilyl.

set bythe consecutive pushes and the resonance@ eiect, inoscillation,andtheseoscillations are radiated forwardly from the V resonance board,vlike from a diapiuagm of. very large dimensions,

" by `far more energically ,than the ,small conical.V

diaphragm is! able to do. The;low4frequency i;

airV osciilations produced by this latter da# phragm serva-therefore,-chiefly to cause oscillat'ionsof an essentially larger diaphragm-,theresonance board-that.V is more capable to .drive those oscillations inforward direction. 1.

`The faction'` of the diaphragm 1 during the possible. V'that everystring is attached to the resonance reproduction of lower ranges ofsoundsV can,

more and more rectilinearly, the share of thel resonance board asregards the forwardly'radiated air oscillations becomes smaller,whereas,-

the share of the diaphragm increases inthe same measure. In the higherpitches of sound the totality of the air oscillations is produced in thediaphragm, whereas vthe resonance board (apart, of course, from theoscillations vcausen by the strings) is practically ineffective.

Figs. l and l2show also diagramatically the housing of the receptiondevice within the box. 1l is the receiver. At the place l2, in thelowerportion of thebox, is the amplier with the 'power supply unitarranged therein. All this apparatus may be madeeasily accessible, asthe rigid part of the"V box may have closable openings `like anyordinary radio chest. 131 denotes protective covers which when beingopened serve as lateral extensions of the rigid wall.

. As'appears from Fig. 1, the Ystrings are subdivided into two sets orgroups in which they are located'in closev proximity to one another..`

The two groups cross oneanother just over the centre of `the diaphragm,and kat this crossing:

point all strings are held fast. by a connecting member which, asshowninthe perspective representationl Fig. 43,' consists of two clampingcheeks 14 and 15 having suitable groovesicr `the reception Vof theindividual strings. I wish it, however, to be understood that I haveshown this `constructional form of said members 14 and 15` only by wayof example; their conigu The justdescribed manner of connecting the`strings with one another by means of connecting members of low weight isan important feature; advantage is this that every string or, moreprecisely, every pairY of strings, is tensioned completely independentfrom all other strings orv pairs of strings, and can, therefore, also betuned perfectly independent The strings are clamped fast between theclamping cheeks'only i' after the tuningY has been finished. From thismoment the halves of every string operate, of course, like independentstrings.

Instead of arranging the strings only in two groups, as shown in thedrawings, they may be subdividedl into more than two groups, andstretched, as in the first described case. Also other modications ofthat tensioning form are The main point in all cases is this the otherFigs. 1 and 2.

another feature entailing an important body at bothiitsends and isdemented in its middle portion with' asuitably designed couplingdevice.` I

. TheY elastically yieldable coupling member 2OV mentioned in the firstpart of this .specification is arranged, as shown in Fig. 2, betweenthe` clamping' device for the strings and .the'drivingv unit.. Thearrangement and combination. of

these parts appearsparticularly distinctly'from Fig. 4, in `whichvthepartszconcerned'are` drawnf The diaphragm l'is con.

to an enlargedscale. nected in the usuallmanner with the oscillatorycoil 2l. A transverse ledge 22 consisting,

for instance, of wood connects said coil withga` metallic pin 23, the`front end' of whichis en' larged so as to forma sort of head.. Thefront" end or" this pin4 and the rear end of asimilarly shaped pin 24are connectedwithone another by means of a coupling element20consisting4 of rubber and having` for j-instance' cylindrical shape;the ends of the two pins t closely into ff said element 120.- The frontend of-,the pin12fi` is connected 'with vthe coupling cheeks 14, andVappropriately the possibilityis afforded .to -re duce the transmissionof the oscillations to the" strings to the desired degree.

I wish it to'be understood also as regards the arrangement `andcombination o f .parts shownin` Fig. 4 that I have merely shown aconstructional` Many .modications' form by Ywayof example. of'thiselastically yielding coupling-devicelare k'possible without constitutingdepartures'of Vthe respective part of the invention. `Also theconstructionvof the .resonancebody as illustrated in Figs. 1 and 2, inwhich the'reson` ance'wall surrounds the rim of the diaphragm on allsides; is merely'an example which islof par#V ticular value inthosecases in which comparatively small diaphragms co-operate with an elec-1trcdynamic drive; with loudspeakers -of simpler Vdesign where a possiblycompact construction is aimed at from lreasons of low price; a; smallerresonance board arranged only laterallyirom the diaphragm may beprovided.

A constructional form ofthis kind is shown in Fig. 5. 'Ihe principlesembodiedtherein'are completely the same as in the example shown in Alsoinr this case only theffront wall is designed as a resonance boardproper, and is attached to the rigid other part of the box in a mannerpermitting said boardto oscillate as required for the purpose in view.A

There is also in this constructional form provided a rigid lateral wall26 which separates the interior of the resonance `chamber from thdiaphragm. Y g f the rim of said diaphragm and extending laterally fromit; a similarly shaped and similarly arranged resonance boardconstituting with said baffle board a resonance box,v the side walls ofsaid box being attached in part to said baille lli latera11y from it; 'asimilarly shaped and similarly arranged resonance board kconstitutingwith said baile board a resonance box; a rigid exten-v hrounding the rimof' saiddiaphragmsandsep:

arating-itfromV the interior of said resonancebox;vand adriving unitadapted toi-cause saidl diaphragm to oscillate, substantially as setforth.l

board and in part to said resonancel board; a

rigid Wall surroundingtherim of said dia-Y phragm and separating itvfrom. the interior of said resonance box, and a driving unit adapted tocause said diaphragm to oscillate,` substantiallyas set forth.

3. A loudspeaker, comprising, in combination, l a large-sized diaphragm,a baiie-board surround.-

ingthe rim of said diaphragm and extending sion attachedtofthe part ofsaid `baiiie board next to said diaphragm, said extension reachingcloselytosaid resonance board; a! rigid Wallv surrounding the rim ofrsaid diaphragm and separating it from' the interior ofv said resonancebox; and 1a driving unit adapted to cause said kvsimilarly arrangedyresonance board constituting with lsaidfbaiiie board .a resonance box;a rigid extension attached Yto said baiile board, said extensionconsisting oflmetal; a rigid wall surv5. Aj loudspeaker, comprising, incombination,

a large-sizeddiaphragm,' a driving 'unit coupled' with said` diaphragm;.a resonance box surrounding rthe'rirn of. said diaphragm .andextendingflaterally from it similarly to a baiie plate; andY a rigidWallalso surrounding the rim of said diaphragmgand separating it. fromthe interior of said-resonance box, saidrigid Wall being. connected Withsaid driving unit and being at the Sametime adaptedrto serve asv asupportingY frame uniting the diaphragm With the drivingunitgsubstantia-lly as set forth. 'f

.6. Aloudspeaker, comprising, in combination, a large-sized. diaphragm,a rigid'baiie board surrounding the rim of said diaphragm andextendbody; a member connected Withsaid strings, and

strings, a rod connected' at one end With said vends of said rods aretightly inserted without rozegoee;A

ing laterally from it; a resonance vboard arranged in front of saidbaille boardand constituting with it a resonance box; sidewallsattacheddn part to saidbafile board andfin part to said resonance board;a plurality of strings stretchedV oversaid resonanceboard; and a drivingunit adapted to cause said diaphragm, ,asv Well as said strings, tooscillate, Asubstantially as set forth. y vf 7. A loudspeaker,comprising, in combination,` a. large-sized diaphragm; a drivingAunitcoupled with said diaphragm; a resonance body; a pluy rality ofstrings lstretchedover said resonance bodyandjbeing attached- With bothends to it; and means for coupling the middle portions of said stringswithV the moving partY of said driving unit, substantially as set forth.A 1 8. A loudspeaker, comprising, in combination, a large-sizeddiaphragm; va driving unit coupled' With; said diaphragm; a resonancebody;` a plurality. of stringsstretched over said resonance bodyv andbeing reachattacl'ied toit at both ends, said stringsA forming groupsvin which they arearrangedr closely side by side, and said` groupsofstrings crossing one another over thegl vcentre of saiddiaphragm;Vmembers holding ,said` 'groups together at the `placerof crossing, anda` screw connectingsaid members with one an-; otherand coupling themwith the moving partv of said driving unit, substantially as set forth.

9. A loudspeaker, comprising, in combination, aiarge-sized diaphragm; Vadrivingv .unit coupled With said diaphragm; a resonancebcdy; a plu-Vralityy of strings stretched over. said resonance a. semielasticcoupling element aranged between said member andthe movng part ofsaid'driving unit and-being connected With both of themgsubstantially as setforth.VY

10. Ay loudspeaker; comprising,` in combination,'a large-'sizeddiaphragm; aA driving unit coupled with `said diaphragm, a resonancebody, a plurality of strings stretchedl over said resonance body, a.member connected With said member, a similar rod connected withthe'moving part ofsaid driving unit,V anda coupling .element consistingof india rubber of a suitable hardness, into the ends'v of' which thefree..

touching one another, substantially as set forth..

" CI-IAKIR MIDHAT. v

